Abstract 2438: Mechanisms of sensitivity and resistance to Sym004, a novel anti-EGFR antibody mixture, in EGFR mutant lung cancer.

Abstract

Abstract EGFR mutant lung cancers are highly sensitive to first generation EGFR tyrosine kinase inhibitors (TKIs; gefitinib and erlotinib), but resistance invariably develops. In the majority of patients, such acquired resistance is mediated by a second-site T790M mutation in EGFR. Second generation EGFR TKIs, such as afatinib, have minimal efficacy in patients with acquired resistance; by contrast, combinations of afatinib with cetuximab or panitumumab - anti-EGFR monoclonal antibodies - are synergistic in pre-clinical models, and afatinib/cetuximab has shown a 30% response rate in a phase Ib trial for patients with acquired resistance. Sym004, currently in phase II trials, is a novel mixture of two anti-EGFR monoclonal antibodies binding non-overlapping epitopes in the extracellular domain III of EGFR. The primary mechanism of action of Sym004 is thought to be EGFR cross-linking, internalization and degradation of the EGFR from the cell surface. To determine if the combination of afatinib and Sym004 shows greater efficacy against TKI-resistant EGFR mutant lung cancer than afatinib combined with individual anti-EGFR monoclonal antibodies, we are investigating mechanisms of sensitivity and resistance to afatinib plus Sym004 in EGFR mutant TKI-resistant lung cancer. Similar to cetuximab, Sym004 has minimal effect on the growth of EGFR mutant cells in 2D culture. However, Sym004 induces growth inhibition of TKI-resistant PC-9/BRc1 cells (EGFR exon 19 deletion/T790M) in soft agar and xenograft models, and afatinib plus Sym004 is more effective at inhibiting growth than either drug alone. In immunoblotting studies, the combination induces greater decrease of total EGFR than either drug alone or afatinib plus cetuximab. Using Alexa Fluor 488-labeled Sym004 and confocal microscopy, the drug induces more efficient internalization and degradation of EGFR than cetuximab in H1975 cells (L858R/T790M). Additional confocal studies will be performed in other TKI-resistant EGFR mutant lung cancer cells. We are also assessing whether addition of Sym004 to TKIs can prevent or delay the acquisition of T790M-mediated resistance in vitro. Finally, we are developing cell lines from PC-9/BRc1and HCC827/R1 (exon 19 deletion/T790M) xenografts that develop resistance to either Sym004, cetuximab, or combinations with afatinib. Collectively, these studies could provide insights into the biology of EGFR mutant lung cancers and preclinical rationale for a trial with the combination treatment of afatinib and Sym004 in patients with EGFR mutant lung cancer and acquired resistance to TKIs. Citation Format: Catherine Meador, Kadoaki Ohashi, Yumei Pan, Elisa de Stanchina, Mikkel W. Pedersen, Ivan Horak, Michael Kragh, William Pao. Mechanisms of sensitivity and resistance to Sym004, a novel anti-EGFR antibody mixture, in EGFR mutant lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2438. doi:10.1158/1538-7445.AM2013-2438